1. Field of the Invention
The present invention relates to a laser diode including a plurality of light emitting devices such as a two-wavelength laser and a three-wavelength laser.
2. Description of the Related Art
In recent years, in the field of a laser diode (LD), a multi-wavelength laser having a plurality of light emitting portions with different light emitting wavelengths on the same substrate (or base) has been actively developed. The multi-wavelength laser is used as, for example, a light source for optical disk devices.
In such optical disk devices, laser light in the 700 nm band is used for reproduction in a CD (Compact Disk), and is used for recording and reproduction in a recordable optical disk such as a CD-R (CD Recordable), a CD-RW (CD Rewritable), and an MD (Mini Disk). In addition, in such optical disk devices, laser light in the 600 nm band is used for recording and reproduction in a DVD (Digital Versatile Disk). By mounting the multi-wavelength laser on the optical disk device, recording or reproduction becomes available for a plurality of types of existing optical disks. Further, a short-wavelength laser (400 nm band) using a nitride Group III-V compound semiconductor represented by GaN, an AlGaN mixed crystal, and a GaInN mixed crystal (hereinafter referred to as a GaN semiconductor) is realized. Such a laser is in practical use as a light source of higher density optical disks. By realizing a multi-wavelength laser including such a short-wavelength laser, applications can be more widened.
In the past, as a three-wavelength laser device having a GaN laser oscillation part as described above, the following laser device with the following structure has been proposed (Japanese Unexamined Patent Application Publication No. 2003-298193). In such a structure, a GaN semiconductor is grown on a substrate made of GaN (gallium nitride) to form a first light emitting device with the 400 nm band wavelength (for example, 405 nm). Meanwhile, a device with the 600 nm band (for example, 650 nm) formed by growing an AlGaInP semiconductor and a device with the 700 nm band (for example, 780 nm) formed by growing an AlGaAs semiconductor are provided side by side on the same substrate made of GaAs (gallium arsenic) to form a second light emitting device. The first light emitting device and the second light emitting device are layered in this order on a support base (heat sink). Thereby, heat generated in the second light emitting device is diffused from GaN and the support base which have superior heat conductance. In the result, heat release efficiency can be improved.